Anatomy of Intervertebral Disc
Anatomy of Intervertebral Disc
Intervertebral discs are the 23 narrow spongy shock absorbers which fit between the 24 separate bones of the spine. As the nine lower vertebrae are fused together, they do not have a disc between them. Each disc consists of a tough fibrous shock – absorbing pad.
Each disc contains a tyre – like outer band called the annulus
fibrousus. Annulus is a tough material consisting of collagen arranged in concentric rings. It also contains elastic
fibres.
Annulus fibrosus encases the nucleus pulposus. The pulposus is a jelly-like substance. It is made up of water ( 80 to 90 per cent ) , protein and collagen. The disc is protected at the top and bottom by cartilages known as end plates. The nutrition and waste removal from the disc occurs by diffusion of these materials via the end plate.
Functions of the disc.
The disc is an elastic structure. It can get deformed due to pressure or weight but it comes back to the original shape once the pressure or weight is removed. The central pulp deforms but the outer annulus restrains the expulsion of pulp outside the disc. Discs act as cushions, or shock absorbers. Their main job is to protect the joints from wearing out. A disc can withstand severe rise in pressure, for example, lifting something incorrectly can cause disc pressure to rise to several hundred pounds per square inch! A 40 kg. Load transmitted to a disc causes only 1 mm of vertical compression and only 0.5 mm of horizontal expansion.
Nerve roots exit the spinal canal through small passageways between the vertebrae and discs. Pain and other symptoms develop when the damaged disc pushes into the spinal canal and compresses the spinal cord or the nerve roots.
The spine protects the spinal cord. Spinal cord is a part of the nervous system. It transmits electrical signals between the brain and the nerves to the legs, arms, back, and other parts of the body. It runs through a hole in each vertebra. The space it runs through is called the spinal canal. Injury to the vertebra or the intervertebral disc can damage the spinal cord.
The backbone cannot hold itself upright. It needs strong muscles, tendons, and ligaments for support. Tendons attach muscles to bones and ligaments stretch from one bone to another to hold them together. Problem in the muscles, tendons and ligaments are also responsible for the development of back pain.
